This invention generally relates to cleaning apparatus and methods applied to the semiconductor processing arts and more particularly to a cleaning tool for removing contamination including small particles in a critical area such as a wafer chuck and wafer support plate in a photolithographic stepper.
In semiconductor fabrication, various layers of insulating material, semiconducting material and conducting material are formed to produce a multilayer semiconductor device. The layers are patterned to create features that taken together, form elements such as transistors, capacitors, and resistors. These elements are then interconnected to achieve a desired electrical function, thereby producing an integrated circuit (IC) device. The formation and patterning of the various device layers are achieved using conventional fabrication techniques, such as oxidation, implantation, deposition, epitaxial growth of silicon, lithography, etching, and planarization.
Photolithography, for example, a lithographic technique for optically transferring a pattern including semiconductor device circuit features onto a substrate is widely used in the fabrication of semiconductor devices. Generally, photolithography involves the performance of a sequence of process steps, including coating a semiconductor wafer with a photoresist layer, exposing the photoresist layer to an activating light source through a photomask, developing the photoresist layer, processing the semiconductor wafer according to the developed photoresist layer, and removing the photoresist layer. An optical photolithography stepper, including those available from ASM Lithography, Inc., located in Eindhoven, Netherlands, is typically used to expose the photoresist layer. An image of a portion of an integrated circuit (IC) is formed on a small, rectangular piece of glass referred to as a reticle, or photomask. The photomask is placed on the stepper and a reduced image formed therethrough is projected onto a portion of the photoresist layer covering the semiconductor wafer.
Where numerous semiconductor devices are to be fabricated from a single wafer, a mask may be used several times over portions of the semiconductor wafer surface. This is accomplished by using a stepper to index, or step the wafer supported on a wafer stage under an optical system including the mask and projection lens, in the wafer plane by a predetermined pitch. At each step, a portion of the wafer surface including the photoresist is exposed by the optical system, for example, with ultraviolet light, to form an image of the mask in the layer of photoresist. Once the wafer surface has been stepped to expose the photoresist, the wafer is then removed from the stepper and the image developed. Further processing steps follow to create features forming a portion integrated circuit, including repeating the photolithographic process in each layer of a multi-layer semiconductor device.
In operation, at each step, or xe2x80x9ccellxe2x80x9d, the stepper performs a focusing operation, typically by altering the height of the wafer surface to achieve optimal focusing. To achieve optimal focusing over the entire surface of the wafer, the moveable stage, or chuck, on which the wafer rests and the wafer itself must be planar within the focal plane to a high degree of accuracy. For example, a particles smaller than 1 micron resting under the wafer surface between the stage and the wafer are enough to create a non-planer discontinuity or deformation in the wafer surface in the area where even one particle is. As a result, the area where the wafer is deformed will be out of focus causing loss of critical dimension in semiconductor device features. This effect is typically referred to as a xe2x80x9chotspotxe2x80x9d, a xe2x80x9cchuck spotxe2x80x9d or a xe2x80x9cchuck ringxe2x80x9d. Such hot spots result in semiconductor devices with substandard features geometries, causing the entire wafer to be scrapped or the entire wafer reworked to correct the error.
In many cases, the particle that caused the defect adheres to the chuck itself, causing the defocusing error to be multiplied over several wafers until detected by visual or automated optical inspection. Consequently, both productivity and yield are detrimentally affected.
According to the prior art cleaning methods are generally used periodically to clean the wafer chuck. One problem with the prior art methods for cleaning, which generally involve manual methods for cleaning the wafer chuck, is that the cleaning process itself may contribute to particle contamination of the wafer chuck. For example, during the cleaning procedure, the wafer chuck including locating pins for slidably fitting into semiconductor wafer locating notches to hold the wafer in place are cleaned of contamination including loose particles. According to the prior art, the typical procedure is to use for example, a sponge to first wipe the wafer chuck manually with a solvent such as acetone prior to manually applying a cleaning abrasive, for example solid piece of Al2O3, to the surface to remove, for example, oxidation deposits and loosen adhering particles. During this manual process, the cleaning abrasive is typically hand held and abrading action applied to the wafer chuck surface. Frequently, during the manual cleaning process to remove contaminating particles, cleaning abrasive particles are dislodged from the cleaning abrasive causing additional contamination that must be removed in yet another cleaning step performed afterwards. Frequently, the is ineffective in removing all loose particles, including those that fall from the locating pins to the wafer chuck surface which are difficult to reach. As a result, the cleaning process has shortcomings including the additional cleaning step made necessary by use of the cleaning abrasive and the possibility that the manual cleaning process of the prior art will result in particle contamination of the wafer chuck surface from the cleaning process itself thereby leading to localized defocusing during the photolithographic exposure process.
There is therefore a need in the semiconductor processing art to develop an apparatus and method for more efficiently and effectively cleaning a wafer chuck used in a photolithographic exposure process thereby reducing particle contamination levels.
It is therefore an object of the invention to provide an apparatus and method for more efficiently and effectively cleaning a wafer chuck used in a photolithographic exposure process thereby reducing particle contamination levels while overcoming other shortcomings and deficiencies in the prior art.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention provides a cleaning tool for simultaneously abrading a contaminated surface and collecting contaminating particles and a method for using the same.
In a first embodiment of the invention, a cleaning tool is provided including an abrasive surface said abrasive surface including a recessed area forming a collection space; said collection space in gaseous communication with at least one gaseous pathway; said at least one gaseous pathway passing longitudinally through a rotatably adjustable elongated handle rotatably attached to the abrasive member for adjustably varying an orientation angle defined by the elongated handle and the abrasive surface; whereby a suction force may be applied along the at least one gaseous pathway to collect particles loosened by the abrasive surface through the collection space.
These and other embodiments, aspects and features of the invention will be better understood from a detailed description of the preferred embodiments of the invention which are further described below in conjunction with the accompanying Figures.